This application relates to a method and apparatus for providing a fire resistant mount for mounting an auxiliary power unit (“APU”) in an aircraft.
APUs are provided in aircraft, and are utilized as a source of power before the main gas turbine engines are started as well as providing power in flight in the event of an emergency situation. An APU includes a gas turbine engine that drives a gearbox which in turns drives a generator, and other required accessories. The APU is typically mounted in a compartment of an aircraft, such as the tail cone, which may be subject to any number of environmental challenges. As an example, there is potential for exposure to flame, and for simultaneous mechanical stresses imposed by aircraft loads.
The APUs have typically been mounted by a strut system which acts as the structural link between the aircraft structure and the APU. Traditionally the aircraft strut system is mechanically fastened directly to an aluminium gearbox housing for 2 of the 3 APU mount points.
Due to updated certification requirements, APU mounts are now required to be fire resistant, and in the case of a fire, APU mounting points must withstand certain loads to get the aircraft home. With the aircraft strut system attaching directly to an aluminium housing in traditional designs, it has been found that the aluminium material does not possess the properties to withstand exposure to flame for the required allotment of time, thus driving designs to implement thermal blankets as a method of protecting mount attachment points from the extreme temperatures imposed by a flame.
As various fire resistant blankets have been implemented into designs to protect the connection point between the strut system and the gearbox, these designs are not preferred for future use if they can be avoided. While the blankets ensure a fire resistant mount attachment point, they present many challenges/issues. Blanket designs are traditionally of complex geometry, costly, have a significant weight impact, are difficult to maintain, and require customer installation due the attachment methods used.